There are two general styles of pliers. The first style of prior art pliers is generally known within the tool trade as a slip-joint pliers or tongue-and-groove pliers as popularized by Channellock, Inc. The second style of prior art pliers is known as a plier-wrench since it combines features of both pliers and wrenches. For the purpose of this invention disclosure the term pliers describes a hand tool in which the jaws are pivotable about an operative axis. The term plier-wrench describes a hand tool in which the jaws may be tightened onto an object, and where the jaw faces are maintained in a parallel relationship with each other. An example of the latter tool is manufactured by Knipex.
Prior art slip-joint pliers are very popular with professionals, hobbyists, and homeowners alike. This style of pliers has enjoyed a wide acceptance because of the ease, speed, and effortless manner with which the jaw gap settings may be changed, even with gloved hands. Also, this style of pliers has a relatively large range of available jaw gaps which allows one tool to be used for a variety of applications. A still further attraction is that these tools are not expensive to manufacture. Within this tool category, there are a number of product choices. Different jaw orientations are available depending on the particular needs of the user. One popular style of slip-joint pliers affords a jaw orientation, which enables easy access to the object being gripped. A second style, known as a “Nut Buster” by Channellock, Inc. permits a higher clamping force on the object, but has an awkward jaw orientation which renders the tool impractical for many applications.
While the slip-joint pliers are a popular tool, one drawback that applies to all slip-joint pliers is that there are relatively few selectable jaw positions available to the user. Consequently, depending on the size of the object being grasped by the pliers, the handle separation distance is often too great for a comfortable and safe, or an ergonomic, hand grip thereon. A poor, or non-ergonomic, hand grip also contributes to a lower jaw clamping force being applied to the gripped object. This lower jaw clamping force can allow slipping of the pliers' jaws on the workpiece when a torque is applied to the workpiece (i.e., nut, bolt, pipe, rod, etc.). A further drawback of the prior art slip-joint style of pliers are the frictional drag and wear associated with the arced tongue and grooves engagement means between the two jaw-handles.
Yet another prior style of tool is the prior art plier-wrench, which is a two-handled parallel-jaw wrench that has the general overall shape and appearance of pliers. The smooth-faced jaws of this hand tool maintain the jaws in a parallel relationship with respect to each other while being opened and closed, in the manner of wrenches. However, the prior art plier-wrench is two-handled in the manner of pliers.
The prior art plier-wrench has five primary parts: an operative (pivoting) handle, a selectable jaw gap setting pivot pin, a leaf spring, a movable jaw, and a one-piece jaw-handle. The jaw-handle consists of a handle and jaw at opposite ends separated by a medial section. The medial section has a slot where both of the elongated interior edges of the slot are toothed. The pivot pin is toothed as well, along a portion of its length and is designed to simultaneously engage, on its opposite sides, the comparably toothed slot. The medial section of the jaw-handle part also consists of two tongues (one on each side of the jaw-handle, in an opposed relationship) which cooperate with matching grooves on the opposed interior surfaces of the movable jaw. The tongues and grooves in the plier-wrench restrict the movable jaw to a straight-line motion while maintaining the jaws in parallel alignment when the jaws are tightened onto the workpiece. The lines defined by the matching tongues and grooves is parallel to the centerline of the slot. The slot and tongues are adjacent to each other, separated by a short distance.
In operation, the prior art plier-wrench operative pivot handle pivots at any one of a finite number of user-selected pivot points along a line which constitutes the slot's centerline. Two tangs which project away from the operative handle's pivot, on either side of the one-piece jaw-handle, engage a pair of mating recesses in the movable jaw. The movable jaw, therefore, is made to move in a rectilinear fashion along a path defined by the lay of the tongue and groove engagement between the movable jaw and the medial section of the stationary jaw-handle, while, the operative handle is made to rotate, or pivot about a point during a tightening, grasping, or clamping action. Because the operative handle only rotates during a tightening action, the short tang lever arms must be of a sufficient length in order to provide a satisfactory jaw travel distance. Therefore this wrench has practical limits in regard to how short the tang lever arms can be made. As a consequence, the mechanical advantage potential of this wrench design is similarly limited.
A force augmentation, or force multiplication, of the prior art plier-wrench at its jaw is achieved by means of the lever arm principle which states that input torque must equal output torque. Torque is defined as the product of the normal force applied to, or exerted by, a moment arm and the distance from the fulcrum at which the force acts. The input torque applied to the hand-grips, at the end of the handles, can be expressed as: Force1×Moment Arm1 while the output torque of the short tang can be expressed as: Force2×Moment Arm2, where the Moment Arm1 is longer than the Moment Arm2 by several times. When the two expressions are set as an equality, it can be easily seen by those knowledgeable in the art, that the force exerted by the tang onto the operative jaw will be several times that of the hand grip force applied to the operative handle at a distance of Moment Arm1.
While the prior art plier-wrench design permits jaw clamping force multiplication over other simple lever plier designs (due to a larger Moment Arm1/Moment Arm2 ratio), its' design has a number of drawbacks. These drawbacks include: the cost of manufacturing, due to the complex parts, is high; the tongue and groove design is prone to dirt contamination; the jaw gap adjustment procedure is cumbersome to operate; and, the force transfer means between the operative handle and movable jaw is inefficient. In particular, the tongue and groove approach used by the plier-wrench contributes to high manufacturing costs and a tendency for dirt and other small debris to become trapped within the blind recesses and tight clearances therein. Debris within the tongue and groove feature interferes with its smooth movement and can make jaw gap changes extremely difficult. Also, it is difficult to clean such plier-wrench due to the blind recesses and welded jaw construction. As a result, this style of plier-wrench is not suitable for any type of dirty work conditions.
Yet another drawback is that making jaw gap adjustments is a cumbersome process when compared to the familiar and effortless sequential rotate-slide/shift-rotate method used by slip-joint plier manufacturers. The prior art plier-wrench requires depressing the pivot pin button (against the resistance of the leaf spring), and while holding the pin depressed, sliding the operative handle and engaged movable jaw to a new jaw gap position. Once the pivot pin is positioned at the new jaw gap position, the pivot pin button is then released. While the sequential rotate and slide method is advantageous since experienced users can perform jaw gap changes with that style of pliers single-handedly, with gloves; it is more difficult to perform a jaw gap change, single-handed, with the plier-wrench, whether or not gloves are worn, particularly, if the pin does not depress easily because of dirt.
Other drawbacks relate to the inefficient force transfer design of the tangs and their respective engagement slots in the movable jaw of prior art tools, including, for example: limitation of the jaw force multiplication factor (mechanical advantage), or conversely, limitation of the jaw travel during a tightening action; increased wear and friction; a “disconnected” feel between the handle and jaw; and, the need for a wide medial section to accommodate the side by side arrangement of the movable jaw and operative handle.
Still another drawback is that the prior art plier-wrench design is inefficient in regard to the translation of a rotary motion (operative handle) to a rectilinear motion (movable jaw). The plier-wrench handle's pivot axis remains fixed while its tangs travel through an arc, which is, in turn, coupled to an engagement slot, which only travels in a straight line, as determined by the movable jaw's tongues and grooves. As described previously, the practical tang length required for such design unnecessarily limits the mechanical advantage potential of the two-piece jaw-handle. Additionally, the tangs and their engagement slots in the movable jaw are a prime source for frictional wear.
Yet another drawback of the prior art plier-wrench design is the “disconnected”, or sloppy, feel between the operative handle and its movable jaw. This disconnected feel worsens as wear opens up the clearance between the respective parts.
A still further drawback of the prior art design is the unwieldy, wide, medial section of the jaw-handle part which is needed for a side-by-side arrangement of the tongues and the elongated slot's centerline.